Elliptical Nozzle Research Articles

Design and Analysis of Elliptical Nozzle in AJM Process using Computational Fluid Dynamics

Abrasive jet machining (AJM) is a micromachining process, where material is removed from the work piece by the erosion effect of a high speed stream of abrasive particles carried in a gas medium, which are emerging from a nozzle. Abrasive machining includes grinding super finishing honing, lapping polishing etc. The common nozzle shape presently used in AJM machining process is rectangle and circular shape nozzle which gives a low flow rate and further demands on decreasing the material removal rate (MRR), so this research mainly focuses on designing nozzle geometry to improve flow rate and MRR in AJM machining process. The elliptical shape nozzle has been designed and analyzed using computational fluid dynamics software (CFD). CFD is the most efficient software for flow rate analysis. The result shows the improvement in flow rate about 574.2m/sec and MRR of newly designed nozzle geometry i.e elliptical shape in abrasive jet machining.

An investigation into the effect of nozzle shape and jet pressure in profile creepfeed grinding

An experimental comparison of cutting fluid delivery nozzles was carried out with application to profile creepfeed grinding. A novel method of nozzle design and development involving rapid-prototyping enabled an exhaustive experimental approach. Circular, rectangular, and elliptical orifice nozzles were compared in terms of workpiece profile error, workpiece surface roughness, and grinding power over a variety of workpiece feedrates and cutting fluid jet pressures. For the grinding conditions used in this research, it was observed that, although the circular nozzle performed best, higher nozzle inlet pressures yielded smoother workpiece surface finishes.

Effect of Nozzle Geometry on Characteristics of Submerged Gas Jet and Bubble Noise.

Submerged exhaust noise is one of the main noise sources of underwater vehicles. The nozzle features of pipe discharging systems have a great influence on exhaust noise, especially on the noise produced by gas-liquid two-phase flow outside the nozzle. To study the influence of nozzle geometry on underwater jet noises, a theoretical study was performed on the critical weber number at which the jet flow field morphology changes. The underwater jet noise experiments of different nozzles under various working conditions were carried out. The experimental results implied that the critical weber number at which the jet flow transformed from bubbling regime to jetting regime was basically identical with the theoretical analysis. In the condition of jetting regime, the generated cavity of elliptical and triangular nozzles was smaller than that of the circular nozzle, and the middle- and high-frequency bands increased nonlinearly. The radiated noise decreased with the decrease in nozzle diameter. Combined with theoretical analysis and experimental research, three different submerged exhaust noise reduction devices were designed, and the validation tests proved that the noise reduction device with folds and diversion cone was the most effective.

Experimental and theoretical investigation of the influence of liquid droplet size on effectiveness of online compressor cleaning for industrial gas turbines

The effectiveness of online compressor washing is site specific and it is determined by several factors, amongst which is liquid injection droplet size that relates to the nozzle orifice diameter and injection pressure. To investigate the influence of liquid injection droplet size on the effectiveness of online compressor washing, three elliptical flat fan nozzles with different orifice diameters were selected, followed by ascertaining the mean droplet sizes for each of the nozzles with the Malvern Spraytec Particle Analyzer. Two of the three nozzles that generated droplet sizes of 55 and 80 μm were employed to investigate the influence liquid injection droplet on the online compressor washing effectiveness. Prior to the washing effectiveness investigations, the three middle blades of the cascade were fouled in a uniform and repeatable manner, after which washing was conducted with different injection droplet sizes. When the washing effectiveness for droplet sizes of 55.1 and 80.24 μm were compared on the aerodynamic performance plots of exit flow angle, total pressure loss, and non-dimensional velocity; a slight difference was observed for the two droplet sizes. The washing effectiveness of using liquid injection droplet size of 80.24 μm produced a lower exit flow angle and total pressure loss coefficient than the droplet size of 55.1 μm. This implies that the droplet size of 80.24 μm has a higher momentum, thereby dislodging the particles more easily than the 55.1 μm droplet size. The reduction in isentropic efficiency and flow capacity obtained from the experimental data for the fouled and washed cases were used as input into Turbomatch to simulate the effects of washing with different fluid injection droplet sizes. Blades washed with a droplet size of 80.24 μm produced a higher recovery of power output and efficiency from the fouled case than the ones washed with a droplet size of 55.1 μm.

Exit Geometry Effect on Jet Mixing

An elliptical nozzle of 3:1 aspect ratio (AR) issuing a Mach 1.5 jet has been used to investigate its mixing promoting efficiency under over-expanded and under-expanded conditions at the nozzle exit. Azimuthal asymmetry of the elliptical shape is interpreted as a benefit to the mixing process, which is significantly enhanced in comparison to an equivalent circular jet under identical conditions. The elliptical jet decays faster than its circular counterpart throughout the jet field. It is found that continuous variation in the size of the mixing promoting vortices shed from the nozzle exit, as a result of its azimuthal asymmetry, is responsible for faster decay of elliptical jet. The visualization of elliptic jet corroborates the fact that the waves prevailing in the elliptical jet are significantly weaker than those in the circular jet.

An experimental investigation on mixing enhancements in non-circular sharp-edged nozzles using the entropy production concept

An experimental study on mixing enhancement in free jets, issuing from sharp-edged nozzles of different geometry, is performed by using particle image velocimetry. The attention is focused on the jet near-field and interaction zones (0 < X/D < 18, where X is the axial coordinate and D the diameter of the equivalent circular jet). The mixing efficiency is evaluated and quantified using the definition of entropy production derived from the velocity field. The effect of Reynolds number is also discussed by performing measurements at Re = 8000 and Re = 35,000. The results are compared to circular nozzle data to evaluate the change in mixing efficiency among axisymmetric and non-symmetric nozzles. While the effect of Reynolds number on mixing is small, at least for the values tested here, the change in geometry is rather crucial. In terms of entropy production, the rectangular and elliptical nozzles show higher mixing for X/D< 7, whereas the other ones attain the best results for larger distances. This behaviour is basically related to the axis-switching phenomenon observed in elongated jets. Different variables are tested and compared as possible velocity and length scales to derive a meaningful non-dimensional entropy production.

Pinch-off of non-axisymmetric vortex rings

AbstractThe formation and pinch-off of non-axisymmetric vortex rings is considered experimentally. Vortex rings are generated using a non-circular piston–cylinder arrangement, and the resulting velocity fields are measured using digital particle image velocimetry. Three different nozzle geometries are considered: an elliptical nozzle with an aspect ratio of two, an elliptical nozzle with an aspect ratio of four and an oval nozzle constructed from tangent circular arcs. The formation of vortices from the three nozzles is analysed by means of the vorticity and circulation, as well as by investigation of the Lagrangian coherent structures in the flow. The results indicate that, in all three nozzles, the maximum circulation the vortex can attain is determined by the equivalent diameter of the nozzle: the diameter of a circular nozzle of identical cross-sectional area. In addition, the time at which the vortex rings pinch off is found to be constant along the nozzle contours, and independent of relative variations in the local curvature. A formation number for this class of vortex rings is defined based on the equivalent diameter of the nozzle, and the formation number for vortex rings of the three geometries considered is found to lie in the range of 3–4. The implications of the relative shape and local curvature independence of the formation number on the study and modelling of naturally occurring vortex rings such as those that appear in biological flows is discussed.

A computational investigation on the influence of the use of elliptical orifices on the inner nozzle flow and cavitation development in diesel injector nozzles

In this paper a computational study was carried out in order to investigate the influence of the use of elliptical orifices on the inner nozzle flow and cavitation development. With this aim, a large number of injection conditions have been simulated and analysed for 5 different nozzles: four nozzles with different elliptical orifices and one standard nozzle with circular orifices. The four elliptical nozzles differ from each other in the orientation of the major axis (vertical or horizontal) and in the eccentricity value, but keeping the same outlet section in all cases. The comparison has been made in terms of mass flow, momentum flux and other important non-dimensional parameters which help to describe the behaviour of the inner nozzle flow: discharge coefficient (Cd), area coefficient (Ca) and velocity coefficient (Cv). The simulations have been done with a code able to simulate the flow under either cavitating or non-cavitating conditions. This code has been previously validated using experimental measurements over the standard nozzle with circular orifices. The main results of the investigation have shown how the different geometries modify the critical cavitation conditions as well as the discharge coefficient and the effective velocity. In particular, elliptical geometries with vertically oriented major axis are less prone to cavitate and have a lower discharge coefficient, whereas elliptical geometries with horizontally oriented major axis are more prone to cavitate and show a higher discharge coefficient.

Near-field structure of underexpanded elliptic jets

Quantitative measurements of velocity for a low aspect ratio underexpanded elliptical jet are presented. Four jets at nozzle pressure ratios NPR = [2.2, 2.6, 3.4, 4.2] are studied for a smoothly contoured elliptical nozzle with an aspect ratio a/b = 2. High-resolution planar particle image velocimetry is used to extract information about the velocity fields and turbulent statistics. All four jets display the expected axis switching phenomenon, with the axis switching gaining strength with increasing pressure ratio. Evidence of regular reflection is seen for jets at pressure ratios of 2.6 and above. Measurements of fluctuating velocity indicate an oscillatory flapping mode in the minor axis plane for all but the highest pressure ratio. At the highest pressure ratio of NPR = 4.2, there is evidence of a cut-and-connect vortex bifurcation previously only observed for jets with higher aspect ratio.

Particle image velocimetry investigation on mixing enhancement of non-circular sharp edge nozzles

An experimental study using Particle Image Velocimetry (PIV) on free jets issuing from different orifice plate (OP) nozzles is reported. Mean velocity, turbulence intensity and higher order profiles relevant for large and small scale mixing are considered in the near field and interaction zone (0<X/D<20). This is done to determine mixing enhancement due to rectangular, squared, elliptic and triangular nozzles in comparison to circular nozzle results in two orthogonal planes. The effect of Reynolds number on the differences among the nozzle shapes is also considered by performing measurements just after laminar–turbulent transition (Re=8000) and in the fully turbulent regime (Re=35,000). The results at low Reynolds number show two classes of jets, i.e. at one side, those closer to axial-symmetric conditions, as circular, square and triangular jets, whereas on the other side those with elongated nozzles as rectangular and elliptic. The reason for the different behavior of the latter is connected to the phenomenon of axis-switching which allows a rearrangement of turbulence over the different velocity components and directions. However, for the highest Reynolds number investigated, all nozzles show similar behavior especially in the jet far field (X/D>10), thus suggesting a significant Reynolds number dependence of the results.

Experimental and numerical study on the inlet nozzle of a small squirrel-cage fan

The squirrel-cage fan performance is sensitive to the inlet nozzle configuration. In this paper, an experimental study combined with numerical simulation has been conducted to investigate the effects of the geometry and the installation of the inlet nozzle on the aerodynamic and acoustic performance of a small squirrel-cage fan. Both the eccentric inlet nozzle and the elliptical inlet nozzle with different levels of the eccentricity ratio and the attitude angle have been tested to search an optimal assembly to improve the aerodynamic and acoustic performance of the studied squirrel-cage fan. Based on the experimental result, three-dimensional steady viscous flow fields in the squirrel-cage fan have been simulated to reveal the flow mechanism of the performance improvement. The result indicates that an optimal elliptical inlet nozzle can reduce flow loss before fluid entering into the impeller passages and induce a tip flow pattern, contributing to promote the volume flow rate and suppress the leaking flow loss.

Experimental investigation on reduced exposure to pollutants indoors by applying wearable personalized ventilation

A wearable personalized ventilation unit able to improve inhaled air quality and reduce risk from airborne disease contamination is reported. The performance of the personalized ventilation device relies on control over the flow interaction near the face of a person by inserting a reduced amount of clean air into the breathing zone. Experiments at 23°C (73.4°F) were performed in a full-scale test room with a breathing thermal manikin resembling a seated occupant in a state of thermal comfort, with a realistic free convection flow around the body and breathing cycle. The room air was mixed with tracer gas. The personalized ventilation supplied isothermally clean air from circular or elliptical nozzles of different diameters (equivalent diameter: 0.025–0.035 m [0.08–0.12 ft]) positioned near the mouth of the manikin. The enhancement of inhaled air quality was studied by varying the initial velocity (0.2–0.6 m/s [0.66– 1.97 fps]), the distance between the nozzles and the mouth (0.02–0.06 m [0.07–0.2 ft]), or the direction of the jet (front, side, or below). The personalized ventilation made it possible to increase up to 94% the portion of clean air into the air inhaled. A wearable personalized ventilation unit can significantly reduce (more than six times) the number of secondarily infected occupants compared to mixing ventilation.

On the vortex structures and behaviour of notched elliptic jets

An experimental study on jets issuing from symmetrically notched elliptic nozzles is reported here, where changes in the flow behaviour due to the notch orientation (i.e. along the major- or minor-plane, known as nozzles A and B respectively) are investigated as part of the overall understanding. Results show that for both notch orientations, the vortex filaments follow the nozzle contours closely immediately after they are formed. For nozzle A, rapid entanglement and stretching of braid filaments by vortex filaments produce vortex-loops along the jet centre region which promote jet entrainment. For nozzle B however, vortex filaments retain outlines resembling the nozzle exit contour the furthest before streamwise vortices with opposite rotational senses are produced. Rib structures are produced by nozzle A but not in nozzle B. Compared to a non-notched nozzle, formations of rib structures/streamwise vortices are accelerated and delayed for nozzles A and B respectively. Additionally, nozzle A is also observed to suppress axis-switching behaviour while nozzle B merely delays it. Furthermore, nozzle A produces larger changes to the momentum thicknesses along both major- and minor-planes. Lastly, compared to the reference nozzle, nozzles A and B produce faster and slower decays of the centreline velocity respectively.

타원형 노즐의 내부유동 구조가 액주분열에 미치는 영향

An experimental study was performed to investigate the liquid jet breakup of a circular nozzle and elliptical nozzles. Furthermore Numerical simulation was attempted to investigate the internal flow structure in the circular and elliptical nozzles. This study showed that the disintegration characteristics of the liquid jet of elliptical nozzles were much different from those of the circular nozzle. The liquid jet issued from the elliptical nozzles became more unstable at the same injection pressure. Surface breakup was observed at the jet issued from the elliptical nozzles with the increase of injection pressure. The disintegration of the liquid jet of elliptical nozzles was related with the internal flow structure which is revealed from the numerical simulation.

Passive and Active Methods for Enhancing Water Quality of Service Reservoir

AbstractKnowledge of flow pattern and water age distributions in service reservoirs is of the utmost importance for ensuring water quality supplied to the customers. In this article, a balancing reservoir was first investigated as a benchmark case. Using the computational fluid dynamics (CFD) method coupled with dynamic meshes, the flow pattern and water age distributions in the reservoir were simulated under actual service conditions. The calculated flow pattern indicated the migration and evolution of flow recirculation regions in the reservoir, which would lead to nonuniform lateral and vertical distributions of the water age, and therefore residual chlorine concentration. A passive flow control method, by adjusting the original circular nozzles to elliptical nozzles, was explored to enhance the water quality. It was found that using elliptical nozzles could assist fluid mixing in the reservoir. The water in the modified reservoir with elliptical nozzles had 5% lower age values than those of the origin...

NUMERICAL STUDY OF ELLIPTIC AND COAXIAL JETS WITH VARIABLE DENSITY

In the present study, the effects of inlet elliptic and coaxial jet geometry on the mixing process with large density differences has been investigated numerically. The coaxial jets are produced through circular and elliptic nozzles. The elliptic and circular nozzles have approximately the same exit area. A second-order Reynolds stress model (RSM) is used to investigate variable density effects in coaxial turbulent jets. Comparative studies are presented for the calculations of the variables. The results indicate that the elliptic coaxial geometry noticeably enhances mixing in comparison with the circular case.DOI: http://dx.doi.org/10.5755/j01.mech.18.5.2693

Experimental Studies on the Effects of Nozzle Structures on Characteristics of Submerged Gas Jet Noise

The structures of nozzle outlet have great effects on jet noise generated by submerged gas jet. Five nozzles with different cross-sections were designed to study the influences of nozzle structures on sound levels by experimental methods. The flow characteristics and sound pressure levels were measured and the gas-liquid flows formed by submerged gas jets under different Weber numbers were also observed. The results show that the gas-liquid flows transformed from bubbling regime to jetting regime with the increase of Weber numbers. With respect to bubbling flow, no significant differences in sound levels for different nozzles were found. However, a remarkable increase of acoustic emission was caused by the transformation of flow patterns over the frequency bands of 0.6-4 kHz for all nozzles. In addition, sound pressure levels for elliptical nozzle were much lower than those of other nozzles over the frequency bands of 0.6-4 kHz. Therefore, it would be a reasonable strategy to adopt several elliptical orifices instead of round nozzle to reduce the gas jet noise in the design of underwater exhaust muffler.

Vortex Behaviour and Velocity Characteristics of Jets Issuing from Hybrid Inclined Elliptic Nozzles

An experimental study on elliptic nozzles with hybrid flat- and inclined-sections is reported here. The hybrid flat and inclined sections are imposed along either the major- or minor-plane of the nozzles (HIN A and B nozzles respectively). For HIN A, results show prevalent pairings between adjacent vortex filaments and induced vortex-loops in the immediate vicinity of the flat-section to produce coalesced vortex roll-ups. Once they detach entirely from the nozzle, they proceed to undergo flow changes resembling that of conventional elliptic jets. HIN B also leads to near-field vortex pairings but produce discrete inclined vortex roll-ups instead, with accompanying delay in rib structure formations. The roles of induced vortex-loops are significantly more limited in the present elliptic HIN than circular HIN investigated previously, due to the dominance of elliptic braid vortices. HIN A produces significantly larger centerline velocity decay, as well as higher turbulence levels in the near vicinity of the nozzle exit. Vectoring of axial jet momentum is more apparent for HIN B, where cross-stream entrainment is also relatively larger. Half-jet width results also demonstrate that both nozzle types eventually produce elliptic jets that undergo axis-switching. Lastly, momentum thickness results suggest that the present nozzle lip-modifications significantly enhance mixing characteristics along the plane upon which they are imposed in both HIN A and B.

원형 및 타원형 노즐 내부유동과 외부유동의 상관관계

원형 및 타원노즐의 내부유동과 외부유동의 상관관계를 알아보기 위해 실험적 연구가 수행되었다. 분사압력에 따라 유량, 분무각, 액적크기 등의 외부유동에 관해 관찰하였고, 노즐 내부유동의 유속 및 압력분포 등을 수치해석을 통해 정량적인 결과를 도출하였다. 외부유동의 경우, 동일한 압력조건하에서 타원형 노즐의 경우, 원형 노즐에서 나타나지 않는 표면분열의 분무특성을 관찰할 수 있었고, 수치해석을 통해 노즐 내부의 유동을 분석한 결과, 원형의 경우와는 달리 타원형 노즐의 단축에서 내부유동의 재부착이 노즐 벽면에서 발생되었다. 타원노즐 외부유동의 표면분열이 내부유동에 따른 결과라고 판단된다.

Numerical investigation on the mixing process in a steam ejector with different nozzle structures

The effects of different nozzle structures on the performance of a steam ejector have been investigated numerically with the computational fluid dynamics (CFD) technique. The performance of the steam ejectors with five different nozzle structures, namely, conical, elliptical, square, rectangular and cross-shaped nozzles, have been compared under the same conditions. It is found that, compared with the CFD results of the ejector equipped with the conical nozzle, the entrainment ratio (ER) and critical back pressure (CBP) of the rectangular nozzle is 7.1% and 21.3% lower respectively; the ER and CBP of the elliptical nozzle is 7.9% and 21.3% lower respectively; the square nozzle has improved the ER by 2.0% and decreased the CBP by 2.1%; the ER and CBP of the ejector utilizing cross-shaped nozzle is 9.1% higher and 6.4% respectively lower. Based on the simulation results of the streamwise vortex and spanwise vortex distributions in the mixing chamber and the internal energy variations along the streamwise distance, the characteristics of the mixing process and the main factors accounting for the ejector performance change are clarified. The ER increase can be achieved by efficient mixing due to the interactions between the streamwise vortex and the spanwise vortex. The streamwise vortex helps to deform and rupture the spanwise vortex which has greater strength. Collides of the vortices to the mixing chamber wall at early stage would increase mechanical energy loss and reduce “effective area” for secondary flow to pass through, resulting in great decrease of the ER and CBP. This scenario should be avoided in the design of nozzles.